BULLETIN OF 

IOWA STATE COLLEGE OF AGRICULTURE 
AND MECHANIC ARTS 

Vol. XII DECEMBER 1, 1913 No. 20 


THE USE OF IOWA GRAVEL FOR 

CONCRETE 

BY 


T. R. AGG and C. S. NICHOLS 



BULLETIN 34 

ENGINEERING EXPERIMENT STATION 
GOOD ROADS SECTION 


Ames, Iowa 


Published Tri-Monthly by the Iowa State College ol Agriculture and Me- 
chanic Arts. Entered as Second-class Matter, October 26, 1905, at the 
Post Office at Ames, Iowa, under the Act of Congress of July 16, 1904. 




PURPOSE OF THE STATION 


T^HE purpose of the Engineering Experiment 
* Station is to afford a service, through tests 
and analyses of materials, special investigations, 
evolution of new devices and methods, and ex¬ 
pert advice, first, for the manufacturing and 
other engineering industries of Iowa; second, for 
the urban population of the State in solving the 
technical problems of urban life; third, for the 
agricultural population and industries of the 
State in the solution of their purely engineering 
problems. 


BULLETIN OF 

IOWA STATE COLLEGE OF AGRICULTURE 
AND MECHANIC ARTS 

Vol. XU DECEMBER 1, 1913 No. 20 


THE USE OF IOWA GRAVEL FOR 

CONCRETE 


T. R. AGG and C. S. NICHOLS 



BULLETIN 34 

ENGINEERING EXPERIMENT STATION 
GOOD ROADS SECTION 


Ames, Iowa 


Published Tri-Monthly by the Iowa State College of Agriculture and Me. 
chanic Arts. Entered as Second-class Matter, October 26, 1905, at the 
Post Office at Ames, Iowa, under the Act of Congress of July 16, 1904. 






ENGINEERING EXPERIMENT STATION 

Station Council 


(Appointed by the State Board of Education) 


RAYMOND A. PEARSON, LL. D.President 

ANSON MARSTON, C. E.Professor 

LOUIS BEVIER SPINNEY, B. M. E.Professor 

SAMUEL WALKER BEYER, B. S., Ph. D.Professor 

WARREN H. MEEKER, M. E.Professor 

FRED ALAN FISH, M. E. in E. E.Professor 

JAY BROWNLEE DAVIDSON, B. S., M. E.Professor 


Engineering Experiment Station Staff 


RAYMOND A. PEARSON, LL. D.President, Ex-Officio 

ANSON MARSTON, C. E.Director and Civil Engineer 

LOUIS BEVIER SPINNEY, B. M. E.. . Illuminating Engineer 
SAMUEL WALKER BEYER, B. S., Ph. D.. .Mining Engineer 

WARREN H. MEEKER, M. E.Mechanical Engineer 

FRED ALAN FISH, M. E. in E. E.Electrical Engineer 

JAY BROWNLEE DAVIDSON, B. S., M. E. 

. Agricultural Engineer 

THOMAS HARRIS MACDONALD, B. C. E. 

. Highway Engineer 


MORRIS I. EVINGER, C. E. 

.Hydraulic and Sanitary Engineer 

ROY W. CRUM, B. C. E.Structural Engineer 

JOHN EDWIN BRINDLEY, A. M., Ph. D. 

. Engineering Economist 

AMOS P. POTTS, Cer. Eng.Ceramic Engineer 

T. R. AGG, B. S. in E. E.Road Engineer 

CHARLES S. NICHOLS, B. C. E.Assistant Director 


H. W. WAGNER, B. S. in E. E 


Assistant Engineer in Mechanical and Electrical Engineering 

MILTON F. BEECHER, B. S. in Ceramics. 

.Assistant Engineer in Ceramics and Road Materials 


JOHN S. COYE, S. B.Highway Chemist 

WILLIAM J. SCHLICK, B. C. E.Drainage Engineer 

GEO. W T . ARMSTRONG, B. Ch. E.Assistant Chemist 

HAROLD F. CLEMMER, B. S. in C. E.Testing Engineer 


/ LIBRAKY Or CONGRESS 

RICEIVED 

; JUN i 5 1925 

> f> 

* t 

• * • | 

DOCUMENTS DIVISION 

— 




































TABLE OF CONTENTS. 


Page 


Figure 1. Gravel Testing Outfit. 4 

Introduction . . . .. 5 

Acknowledgments . 5 

Definitions . 5 

General Principles of Concrete mixtures. 6 

Grading ot Aggregates. 6 

Figure 2. Curve of Grading for Gravel.10 

f igure 3. Curve of Grading for 14 inch sana.12 

f igure 4. Curve of Grading for y 8 inch sand.15 

Strength of Concrete . 7 

'table 1. Approx. Av. Crushing Str. of Concrete. ... 7 
Concrete Mixture. 7 

The Sieve Analysis of Gravels. 8 

Gravel Testing Outfit . 8 

Sampling Gravel . 0 

Sieve Analysis .".. 9 

Clay Tests .11 

Concrete made with Pit Run Gravel.13 

Sand .14 

Table II. Illustrative of Well Graded y 8 inch 

Sands .16 

Table III. Illustrative of Poorly Graded y 8 inch 

Sands .18 

Table IV. Illustrative of Poorly Graded y 8 inch 

and y^ inch sands.19 

Cleanness .20 

Gravel Needed for a Cubic Yard of Concrete.20 

Reproportioning Gravels .20 

Figure 5. Curves showing amount of Cement per 
Cubic Yard of Concrete, and Amount of Ag¬ 
gregate per Sack of Cement.21 

Cost with Pit Run Gravel.22 

Figure 6. Cost of Materials for 1:2 :4 Concrete.24 

Cost with Screened Gravel .23 

Figure 7. Cost of Materials for 1:2y 2 :5 Concrete.25 

Cost W r hen Stone is Added.25 

Figure 8. Cost of Materials for 1:3:6 Concrete.27 

Conclusion .26 

Figure 9. Curves showing Amounts of Gravel to 
Screen, and Stone to Add for one Cubic Yard 
of Conerfirt.e.-.f fmy«’ «‘a».2*^ 

* ■ « W.*- MV. V\ **«?**! < 

; ' * '■ i « •• 


v *.. •; V »•*. • .* Xfl l 


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9 



FIGURE 







































THE USE OF IOWA GRAVEL FOR CONCRETE 

INTRODUCTION 

The survey of deposits of concrete materials which has recently 
been completed through a co-operative arrangement between 
the Iowa Highway Commission and the Iowa Geological Survey, 
shows that the gravels are the most widely distributed and 
widely used aggregate. The survey also shows that the composi¬ 
tion of these gravels is exceedingly variable, particularly as 
regards the amount and character of sand they contain. 

As might be expected when such variable materials are being 
used, there is a good deal of variation in the quality of the con¬ 
crete produced. It is for the purpose of supplying in convenient 
form information which will lead to a more economical use of 
gravels and a more uniform quality in the concrete produced, 
that this Bulletin is offered. 

Acknowledgements. In the preparation of this bulletin ref¬ 
erence has been made to various standard works on concrete and 
reinforced concrete, especially to Taylor and Thompson’s “ Con¬ 
crete, Plain and Reinforced,” and to various articles published 
by Messrs. Fuller, Thatcher and Feret. 

The gravels, which are listed in Tables II, III and IV, were 
collected and analyzed under the joint direction of the Iowa 
Highway Commission and the Iowa Geological Survey. 

The curves used to represent the economy of various mixtures 
are developed along the line originally worked out by Mr. 
Clifford Older, Bridge Engineer of the Illinois Highway Com¬ 
mission. 

Definitions. The various terms used in the discussion are 
defined as follows : 

Stone. —That portion of a pit run gravel that is retained on a 
i/4 inch screen. 

Sand. —That portion of a pit run gravel that passes a % inch 
screen, or a % inch screen, as the case may be. 

Pit Run Gravel. —A mixture of sand and gravel in any pro¬ 
portion as it comes from the pit. 

Coarse Aggregate. —Pebbles screened from pit run gravel, or 
crushed stone of a size that is retained on a % inch screen. 

Gravel. —Pit run gravel or screened and graded gravel. 

Crushed Stone. —Broken stone of any character, crushed and 
screened over a *4 inch screen and through a 21/2 inch screen. 

One Sach Cement. —A sack of cement is assumed to be 0.95 
cubic feet. 

Measurements are by volume measured loose; that is, shoveled 
or dumped into the measuring box without tamping or shaking 
down. 


6 


GENERAL PRINCIPLES OF CONCRETE MIXTURES. 

It has been established by numerous experiments that the 
strength of the concrete which is made from any mixture of sand 
and stone depends primarily upon the ratio of sand to cement in 
the mixture, so long as the mortar thus made is sufficient in 
quantity to fill the voids in the stone. The strength of the con¬ 
crete is not increased by decreasing the amount of stone below 
the quantity in which the voids will he just filled, nor is it 
materially decreased. 

The exact strength of a concrete made from a mixture of sand 
and stone will vary considerably with the size and grading of 
the sand and of the stone. If the sand grains are all very small 
and the stone pieces all of the same size, a relatively poor con¬ 
crete will he produced with a given amount of cement. If, on 
the other hand, the sand ranges in size from *4 inch down and 
the stone ranges in size from 2y 2 inches down to i /4 inch, both 
being well graded, a relatively strong concrete can he made 
with a. given amount of cement. 

Grading of Aggregates. Numerous investigations have been 
made to determine the best grading of the coarse and fine aggre¬ 
gates in order to obtain maximum strength in concrete, and 
practically all the investigations that have been made sub¬ 
stantiate the correctness of the theory that an aggregate will 
give the strongest concrete that can he made with a given 
amount of cement if the sand and stone when mixed are so 
graded that the mixture has its maximum density; that is, when 
the various sized particles exist in such a proportion that the 
percentage of voids in the aggregate is the smallest that can be 
obtained with that material. Messrs. Taylor and Thompson, in 
“Concrete, Plain and Reinforced,” give a curve which is a 
practical adaptation of the theory of maximum density, and 
concrete made with aggregates graded so that the percentages 
passing through screens of various sizes will fall on this curve 
will give the densest, and therefore, the strongest concrete that 
can be made with that aggregate. This curve is shown in Figure 
2 . Likewise, considering the best grading for sand and the 
best grading for coarse aggregate, considered separately, it is 
found that the curve for maximum density for mixed aggregates 
can be separated into two parts, one of which represents proper 
grading for sand, as given in Figures 3 and 4. 

There is reason to believe that a good sand should not contain 
to exceed 10 to 15 per cent, of grains that will pass a screen 
having 50 meshes per linear inch; the lower end of the sand 
curve representing cement rather than fine sand grains. 

The possibility of grading aggregates in accordance with 
these curves is somewhat limited and can only be carried out on 


7 


work of such magnitude as to warrant the expense necessary for 
securing the various sized aggregates and properly mixing them. 
On the other hand, for small work it is often possible to approxi¬ 
mate the conditions of maximum density by mixing two or more 
materials and thereby effecting a considerable saving, in the 
amount of cement necessary to give a concrete of the required 
strength, over what would be necessary if poorly graded aggre¬ 
gates were used. 

Strength of Concrete. In contract work specifications com¬ 
monly give the range of sizes of “sand” and “stone” and the 
amount of each that must be used with one part of cement. The 
specifications must provide first that the proper ratio of sand 
to cement shall be used so that the concrete will have the desired 
strength. Just what this ratio shall be depends, to a certain 
extent, upon the character of the sand, but for sand of fair 
quality, that is, clean and fairly well graded (not all fine or all 
coarse, but being a mixture of the two), the strength of various 
mixtures has been determined by numerous experiments. The 
following table of average values is given in Taylor and Thomp¬ 
son’s “Concrete, Plain and Reinforced:” 


TABLE I. 

APPROXIMATE AVERAGE CRUSHING STRENGTH OP CONCRETE. 


Proportions 
by Volume 

Medium Consistency 

Wet Consistency 

Cubes 

Cubes 

8x16 in. Cyls. 

30 Days 
lb. per sq. 
in. 

6 Mos. 
lb. per sq. 
in. 

30 Days 
lb. per sq. 
in. 

6 Mos. 
lb. per sq. 
in. 

30 Days 
lb. per sq. 
in. 

6 Mos. 
lb. per sq. 
in. 

1 

n 

3 1 

2800 

3700 

2600 

4100 

2300 

3600 

1 

2 

4 ! 

2500 

3300 

1900 

3100 

1700 

2700 

1 

n 

5 

2200 

2900 

1700 

270*0' 

1500 

2400 

1 

3 

6 

1900 

2600 

1500 

2400 

1320 

2100 

1 

4 

8 

1500 

2100 

1COO 

1600 

900 

1400 


Concrete Mixtures. In mixing the concrete the cement fills 
the voids in the sand and coats the grains. This mixture is 
called mortar. The mortar thus made binds the stone together 
unless too much stone is used. The volume of mortar made with 
any mixture, except a very lean one, will usually be a little 
greater than the volume of sand used. 

It will be noted in Table I that the proportion of stone is in 
every case twice that of the sand. The proportion of stone used 
does not materially affect the strength of the concrete unless, as 
previously stated, so much is used that there will be insufficient 
mortar to fill the voids in the stone. The amount of voids in 
































8 


graded broken stone from which the dust has been removed or 
in stone screened from gravel seldom exceeds 40%. The mix¬ 
tures given in Table I provide half as much sand as stone and if 
the voids in the stone are 40% they will, therefore, be filled and 
there will be a slight excess of mortar. This excess is desirable 
because in the process of mixing and placing the concrete the 
mortar may not be placed in the most advantageous position in 
the mass, and there will at best be some voids in the concrete 
after it is tamped in place. 

If concrete is to be used for work where a good finish is de¬ 
sired a greater excess of mortar is necessary than the mixtures 
in Table I provide, and the following are often used: 

1-2-31%, 1-21/2-4, 1-3-5, etc. 

The following mixtures are commonly specified for a few 
classes of concrete work. This will serve to indicate in a general 
way the work for which each is suited 

Footings on bridge abutments 
Brick pavement base 

Abutments, piers and headwalls' 

Brick pavement base, founda¬ 
tions 


} 


1-3-6, or 1-3-5. 


1-21/2-5, or 1-21/2-4. 


Reinforced concrete of all kinds, 
such as culverts, tanks, bridge 
floors, walls, one course pave¬ 
ments 

Hand rails, girders, one course 
pavements, one course side¬ 
walks, and work to take a 
good smooth finish 


.1-2-4 


1-2-31/2 


THE SIEVE ANALYSIS OF GRAVELS. 

The first step in the investigation of a gravel is to determine 
the relative amount of sand and stone and the grading of each. 
This is done by means of the sieve analysis. For important work 
upon which a large amount of material is to be used it would 
be desirable to use ten sizes of sieves for the sand and the same 
number for the stone. But for work upon which only a few 
hundred cubic yards of material is to be used it is unnecessary 
to make such a complete analysis of the gravel. A small port¬ 
able testing outfit will usually enable the user to make all of 
the examination required. 

Gravel Testing Outfit. In Figure 1 is shown a gravel test¬ 
ing outfit which is used by the inspectors of the Illinois Highway 
Commission. Similar outfits can be made by any tinsmith for 
about $3.50, or can be obtained from the Iowa Highway Com¬ 
mission at actual cost, which is about $3.50. 








9 


The outfit is made of galvanized sheet iron and galvanized 
screen wire and consists of the following parts: 

B. A y 8 inch sand screen. 

C. A 14 inch sand screen. 

D. A y 2 inch screen for stone. 

E. A measuring vessel 4 inches in diameter and 10 inches 
deep. It has a cover which is shown lying beside the vessel. 

F. A tube for protecting the glass graduate used for clay 
tests. The capacity of the tube F should be 50% that of the 
measuring vessel E, i. e., in the ratio of sand to stone commonly 
specified. 

G. A glass graduate 12 inches high and about 2 inches in 
diameter which is used for the clay test. 

The tube which protects the glass graduate fits inside the % 
inch screen and the three screens nest together and fit inside the 
measuring vessel. The outfit, packed for carrying, is shown 
at A. 

Sampling Gravel. Obviously, the whole value of a test de¬ 
pends upon securing a representative sample for analysis. The 
sample should, therefore, be taken with great care. If taken 
from a stock pile of material, a quantity of gravel should be 
taken from a number of different places in the pile and the 
amount thus secured carefully mixed and spread into a circular 
pile and then reduced to the proper size for testing by repeatedly 
quartering. Several samples thus tested will indicate the ac¬ 
curacy of the results being obtained. If the sample to be tested 
is taken directly from a pit, the appearance of the pit must be 
carefully studied and the sample secured by taking portions 
from different places in the pit in such a manner as to obtain 
a representative sample, and one which will be similar to the 
material which will eventually be hauled from the pit. These 
preliminary samples will be sufficient to indicate the general 
character of the materials, but if the gravel is hauled to a new 
location before being used the preliminary tests should not be 
used as a basis for proportioning the aggregate for concrete. 
When the material has been hauled to the place where the con¬ 
crete is to be mixed it should be examined and tested and exact 
proportions for the concrete determined upon the material which 
is actually to be used in the concrete. It will be found necessary 
to make frequent tests upon the gravel as the work progresses 
if its quality varies to any appreciable extent. 

Sieve Analysis. Having collected a sample of the gravel 
which is thought to be representative, the large sheet-iron 
measure (E in Figure 1), which is 10 inches high, should be 
filled with the gravel to be tested and shaken down until no 
more can be added. If the test is for the determination of the 
proportion of *4 inch sand in the aggregate, then the material 


10 



O./O .30 0.30 0.40 0.50 0.00 0.70 0.80 0.90 /.OO /./O /30 /30 /40 /.50 

Diameters of Fortic/es in /r?cf?es. 

FIGURE 2 




































































































































































































11 


contained in the measure is screened through a 14 inch screen 
and the two fractions thus obtained placed successively in the 
measure, thoroughly shaken down and the amount recorded. 
Since the container is of uniform diameter, the volume will be 
proportional to the height of the material in it. For example, 
if it is found that there are 6 inches of sand in the container, the 
percentage of sand would be 60 and if there were 5 inches of 
the stone the percentage of stone would be 50. These percent¬ 
ages, when added together, give 110%, as will be noted. 

In making the sieve analysis by volumes it will always be 
found that since the fine aggregates fill in the voids between the 
coarse aggregates when the two are mixed together, the sum of 
the volumes of the two when separated will be somewhat greater 
than the volume of the two mixed. Therefore, it will be found 
that the percentage of the two fractions added together will 
range from 110 to 125, depending upon the character and rela¬ 
tive percentages of voids of the two parts into which the pit run 
gravel has been separated. 

If it is decided in addition to determining the proportion of 
sand in the bank gravel, to determine the grading of the sand, 
then the sand itself may he screened through the % inch 
screen and the proportion of material which is retained on, and 
passes through the % inch screen measured, which gives an in¬ 
dication of the grading of the sand itself. Likewise, it may be 
desirable to determine the grading of the coarse aggregates by 
screening it through the % inch screen. If the percentage of 
y s inch sand is desired it can be determined by using the % inch 
sand screen instead of the % inch. By referring to the curves 
in Figures 3 and 4 the grading of the sand can be checked. 

Clay Tests. An approximate determination of the amount 
of clay or loam in an aggregate may be made as follows: Fill 
the glass graduate (G in Figure 1) about half full of the aggre¬ 
gate which is to be tested and then add water until the graduate 
is about three-fourths full, thus leaving a space at the top of 
the graduate unfilled. The graduate is then shaken for at least 
5 minutes so as to give time for the water to wash off all clay 
or loam from the particles of the aggregate. After the grad¬ 
uate has been shaken it is suddenly turned right-side up and 
set aside to allow the clay to settle. The clay or loam will 
settle on the top of the aggregate and may be measured after the 
water clears. The layer of clay thus deposited will vary in 
thickness depending upon the length of time it is allowed to 
settle as it tends to become more compact the longer it stands. 
If the measurement is made soon after the test is completed, 
that is, after it has stood for only a few minutes, a larger pro¬ 
portion of clay will show than if the measurement is made after 
the clay has stood for some time. It has been found by experi- 


12 


ment that if the clay has been allowed to stand for three hours, 
the percentage will then be approximately four times the quan¬ 
tity that would be obtained if the clay should be removed and 
evaporated to dryness. Therefore, it may be assumed for 
ordinary practice that the percentage of clay at the end of 
3 hours is 4 times the dry percentage, and if the limit of clay 
by dry measure is 3 per cent, then there may be permitted by 
the method outlined above, 12 per cent of clay in an aggregate. 
This method is not exact, on account of the fact that water con¬ 
taining clay has settled into the voids of the aggregate in the 
lower portion of the graduate, but will serve unless the test 
thus made shows a percentage of clay near the allowable limit, 
in which case the exact test should be made. 






i 





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$ 

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V. 







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$ 


90 


80 


t 

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60 


£0 


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$ 


40 


X 


20 

JO 


QOS O.JO O.JS 020 

Diameter of Particles in Inches 

FIGURE 3 


025 


If it is desired to get exact results, all the clay must be washed 
out of the gravel, the washings collected together and evaporated 
to dryness. The clay content can thus be accurately determined. 

Value of Sieve Analysis. There are many uses to which the 
sieve analysis is put. One is to determine with a given pit run 
gravel the amount of cement necessary to make concrete to meet 
a given specification. Another is to determine the amount of 
coarse aggregate or fine aggregate to add to a given bank gravel 



















































































































13 


in order to give a mixture graded in accordance with a given 
specification. In other cases the mechanical analysis may be 
used to determine from among a number of available aggre¬ 
gates the one that is best graded, or the best possible combina¬ 
tion of two or more gravels for a given structure or for a given 
specification. 

CONCRETE MADE WITH PIT RUN GRAVEL. 

It frequently becomes necessary to make concrete from pit 
run gravel and it is common practice to specify an arbitrary 
mixture such as 1 to 4, or 1 to 6. 

A 1 to 4 concrete made from pit run gravel from one pit will 
differ in strength very much from a 1 to 4 mixture of pit run 
gravel from some other pit unless the two gravels happen to 
be very much alike as to the sand content. 

A specification such as 1 part cement to 4 parts pit run 
gravel means nothing unless the allowable percentage of sand 
in the pit run gravel is also specified. It is generally assumed 
that a mixture of one part cement to four parts pit run gravel 
is equivalent to a mixture of one part cement to two parts sand 
and four parts stone. As a matter of fact they are not equiva¬ 
lent unless the volume of sand in the pit run gravel is just half 
the volume of the stone. 

It is apparent, then, that in making concrete from pit run 
gravel there must be some basis for proportioning that takes 
account of the varying percentages of sand in the gravel. The 
great variation in this factor can readily be seen by an exam¬ 
ination of Tables II, III and IV, which give the results of 
sieve analyses made on a number of Iowa gravels. 

Referring again to the general principle that the strength 
of concrete depends primarily upon the ratio of sand to cement 
and applying that criterion to the proper proportioning of con¬ 
crete made with pit run gravel, it may be stated that the amount 
of cement to use with any pit run gravel for a concrete of any 
desired strength can only be decided upon after the sand con¬ 
tent of the gravel is known. 

If the pit run gravel is to be used for making the concrete for 
bridge piers or for a pavement base, where a mixture of l-2y 2 -5 
would be specified if crushed stone or screened gravel and sand 
were available, the amount of cement to be used with the pit 
run gravel would be that which would make with the sand in 
the gravel a 1 to 2 y 2 mortar. The amount of stone in the 
gravel does not influence the amount of cement to be used, but 
if the volume of stone in the gravel were more than twice the 
volume of the sand some of the stone should be screened out. 
If the volume of stone in the pit run gravel is less than twice 
the volume of sand that does not materially decrease the strength 


14 


of the concrete, so long as the ratio of sand to cement is kept 
constant. The amount of concrete obtained with a sack of 
cement in this latter case will, however, be less than if the 
volume of stone were just twice the volume of sand, and the 
amount of cement used per cubic yard of gravel would, there¬ 
fore, be greater than if the sand and stone were in the proper 
relative proportion. 

From the foregoing it is apparent that concrete made of pit 
run gravel and cement in proportions arbitrarily chosen with¬ 
out regard to the sand content of the gravel will not be uni¬ 
form in strength nor will its exact strength be known before¬ 
hand. To use such concrete in structures of any magnitude or 
importance is dangerous and uneconomical. Even with the 
greatest care in the selection and grading of the aggregate and 
mixing the concrete there will be some variations in the strength 
of different batches of concrete made at different times, and 
it is important to avoid all known causes of variation in 
strength. 

Sand. Since the amount of sand in a pit run gravel deter¬ 
mines the amount of cement that must be used, it becomes of 
considerable importance to know just what part of the mix¬ 
ture shall be called sand. It has become common practice to 
consider as sand that portion of pit run gravel that will pass 
through a % inch screen, and most plants furnishing sand on 
a commercial scale have their screens arranged in that way. 
If, however, the matter is considered from the standpoint of 
scientific grading of the fine and coarse aggregates (“sand” 
and “stone”) the maximum size of the particles of sand should 
vary with a variation in the maximum size of the pieces of 
coarse aggregate. If the coarse aggregate is graded up to 2 y 2 
inches, then y± inch sand would be the best, but if the coarse 
aggregate is graded up to 1% inch, then sand graded from about 
y 8 inch down would probably be best. 

Since most of the pit run gravel used in Iowa contains very 
little material above iy 2 inch in size, theoretically the sand 
should be graded from about % inch down, but should be 
screened through a larger sized screen for use with crushed 
stone of the 2 inch size, or coarser. It is not necessary or de¬ 
sirable on small work to vary the sand screen for each deposit 
of gravel, even if the maximum size of stone does vary, because 
the grading of the material otherwise is not uniform enough to 
warrant such great refinement in the size of the sand. If sand 
from y 8 inch down is used it should be reasonably well graded, 
that is, it should fall somewhere near the curve for % inch 
sand given in Figure 4. Just how much variation would be 
permissible cannot be definitely stated from the data at hand, 


15 



but good results have been repeatedly obtained when the per¬ 
centage of the % inch sand which passed a 1-16 inch screen 
was as little as 65% and where it was as great as 85%. 

The results of the analyses given in Tables II, III and IV have 
been separated into the three groups on the following basis: 

Group 1, which is listed in Table II comprises pit run gravel 
in which the grading of the % inch sand is within the limits 
above mentioned if screened through a 1-16 inch screen. With 
pit run gravels of this type it is believed that concrete may be 
safely proportioned on a basis of the amount of % inch sand 
contained therein. 

Group 2, listed in Table III, comprises pit run gravels in 
which the % inch sand is poorly graded, that is, the percentage 
of the sand which passes a 1-16 inch screen is either greater 
than 85%, or less than 65%. In the majority of cases it is 
greater than 85%, which is to say that the sand is tine. But if 
the sand is screened through a inch screen it is found to be 
reasonably well graded. Pit run gravel of this type should be 
used with care on important work, the amount of cement used 
being based upon the amount of % inch sand contained. It 
is not safe, in the light of present knowledge, to mix concrete 
on a basis of the % inch sand contained in gravels of this type 
and in any case it would be best to screen and reproportion 
the material. 



















































































































































The following tables are illustrative of the results that may be expected when the sieve analysis is 
made on pit gravel. It should be noted that the per cent of sand and stone has been determined by 
weight and not by volume, and for purposes of comparison the percentage of sand should be used. The 
percentage of stone is not comparable with results of test made by volume measure. 

The column headings are self explanatory. 


16 


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COCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOCOSOGOCOCOCOCOCOCO 

CO CO CO CO CO ©I CO CO CO CO CO CO CO CO CO CO* CO CO CO CO CO CO CN CO CO CM CO CO CO CO CO CM CO CO 4-3 CM CO CO CO 

83S88888S888S88888SS8888888888888888888 


888888888888888888888888888888888888888 


3®88 88S88®8S88g3tete888B®88te8Sg8888ggfc88$S 

G«dedcd-^'cc't'CO'4<'^<cd'j'cv3cci<Neoco'«<^»<'^iMeoec'^<^eocOo5iM-^ieoeCiMoco»i'^i(MeCi 


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Sand to add. 















































TABLE III. 


18 


o 

& 

o 

I—I 

Eh 

<3 

O 

O 


ajajonoo -py -no 
X joj sjBtjaxBj^ eptA 
-oaji ox ppy ox pneg 
jo 900X8 ’SPA -no 


0X0Jonoo 'PA 'no 
I JOJ 'X'BR 9JO008 
OX O90J08 OX I0ABJO 
nna XM 'spi -no 


Cement per Cu. 
Yd. Concrete, Us¬ 
ing Screened and 
Reproportioned 
Gravel 

•iqa 

0G'I$ XSOO 

•SIQH 

SJ[0BS 

Cement per Co. Tel. 
Concrete, Using 
Pit Run Gravel 

•iqa 

02'I$ XSOO 

•siqa 

SiJDBg 

Abio jo aSBXUdDJej 

Voids 

0UOXS 

POBg 

auojs ox 

pUBg JO OJXBH 


U90,ios 

'nr yj-x S-Q'ISSbj 

pOBg JO 0.SBXO0OJ0(I 


(*OI 8-X SUISSBd) 
POBg jo 0SBXO00J0IJ, 


(•OI 8-1 9Aoqy) 
0UOXS J° 9§BX'U'0JJ0 < I 


jaqran^ epItoBg 


PH 

>1 

-4-H 

o 


Ph 

tc 

"5 

cc 


- a 

M o 


£ v 

® r—* 

AG 


a 'o r >> 

gB3r«J^P 

* 


a. 

> 


. A 

-M 

Ph c 

£?a a 

a <v 

•a > . 

c ® >> 

<D Fh Zj 

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2 > G 

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a . « ? p 1 

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S q o 2 2 
S « a "5 • 

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*) 

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to 

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5?5®rHi'i'5HNOiaftmct'l''H7']j'CnC'. MnWHiiN 

© o’ o © d o’ d © o' © © d d o © o o o o © © o’ o © © © 

s 

T—1 

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1.07 

2.31 

i i 

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I hCj© 001>WH00O(N1 O i to to o 

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l 1 

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<Mdc4<Mfr5(NO^d<M<N(N’c<JC<ldoic<l<N’c<]<M<>3c<ie^<NC')03<N 

O 

CO 

T—i 

HHHiHriHHHHrlriHrHHiHHrHrlHrliHHrlrUHH 

✓“H 

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r—1 

S3888888888888888888888888 

coococoto<oto<^cototoccotdtDcdcoototccc>tctdtc>tC'to 

(ID 

2.34 

3.98 

i i 

i<M*3<M(»-Hii'-frioQy5lf5t~t-c<lC©C'21>>A00e'O i CO © © 

iHNr-lOJOOH'MH'OMiOinr-iOOBOlfit'PW l 00 <M 'T 1 

!C<PC<!'0i<NCOMHH(?3ecaPe<ic6-H<e<l<Ni'C>e<5iMCCi ' M M W 

/—s 

e> 

i—1 

'w' 

1.56 

2.65 

I I 

l ^rPt r5 ® { ® r PS»i2coeoi050i05^ifti»©iow iNWO 
iOOOt'5)iqMw®oiNSHMl>&J>coinajN i<mi-^© 

I (M M H 

I 1 


6.25 

10.60 

loi/jQOlOiJOpOOOOCOQOQOO '©OO 

iCOINOCOIN^noCCirHOOWQ^OWO^W 1 o to Hi 
'COt^H^OOiHCOOOOOOiCiHNNOiONOO i CO 00 tC 

• rH t— i rH rH iH 1 

1 1 
i l 

oo 

M00r-llfti~C9e<jC5©'H<-H<©lO©©©»O©-H<'H<©©©©©© 

©J^<MCO'H<CCCOi-H©©r-<©i'-CC>-H<©i''-©C0COiO©LOC'4'H<iQ 

k^5i^t^rH©i^©©cge<5i-HiAccc<ido3-Hi*-iiftAddAcoAcl 

rH iH 

rs 

Jt> 

'w' 

<M O 
H< 


/■"N 

s 

St5 

©©C>©©li2<0lQ^-H'«O00$'10QlOlftrH-«*<DK5lft<M©00 

MKHftC'H»W«MCHW(NI»M{5cCWCii«5HMCOM(NIN 

Lft 

'w' 

g®S88S3ateai;i8S8l8e88?H8SsS8?8g8S8 

ON©HHMHNHHlOr(HHf)MHOciNr-IHdHHd 

HH 

G-' 

i 45 

53 


CO 

'w' 



CM 


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'w' 



Sand to add. 

























































































19 


&< 

O 

o 

hH 

H 

<3 

O 

O 

i-l 


S 

0 > 


03 

M 


tw 

tH 

C3 

s 

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£ 


a i 3 
d'g 
S-9 

I S 

QO 


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02 


£3 53 

oM 

3S 


P4 


>1 

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03 . 0.0 

r=< Xj QjJ • 

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1 +-» 25 ■*-‘ SS ® v 


a 

r£ 

o 

+j 

• • r—t 

m Ct cS 
O ° -C 


> 

HH 

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PQ 


ajaaonoo ’Pi ‘^0 

l JOJ S[BliajBJ\[ 9piA 

- 01*11 oj ppy oj pueg 
jo auojg 'spi -no 

(o 

1—1 
s-/ 

88 28332 §£$838g!gfc§Sgg9gS!2|: 

fc~iAooj^ooooooooooS>f-ooi^t^a)i^(>Ji^e) 6 oooc»oooot^i^c<i 
dodo o’ do o' odd o' o’ odd o' dodo do" ©odd 

ajajouoo ‘Pi - no 

I joj ‘jbw amoag 
oj naaiag oj iaABJ£) 
tma Jfd -spy -no 

/—s 

to 

rH 

' 

7.50 

1.82 

12.00 

6.67 

15.00 

10.00 

60.00 

15.00 

3.00 

6.00 

15.00 

4.61 

4.28 

30.00 

3.16 

5.45 

20.00 

1.07 

30.00 

10.00 

6.67 

3.53 

Cement per Cu. 1 
Td. Concrete, Us¬ 
ing Screened and 
Reproportioned 
Gravel 

qqa 

OS'I# JSO.Q 

rH 

'w' 

rH 

l«iOiQi43kOi2>U3 l O l OU3 l S> l O L O l O l OlOU3u3iO l Q>Otf5iC>K5 l £5iOU5 

NN<NCM<N<NiNcN<N<NoJ<NC'lC<)iN<NNN<N<NCM<NC<ie<l<NC'jN 

in <n 04 <n <n 04 in c<i <n" in d <n d (n d d d d d d d n d d d d 

•siqg 

888888888888888888888888888 
rH rH rH H rl H H rl rl rl rH HHrlHrHrlHrlrHHHHH rH rH rH 

SJjUBg 

✓-n 

tH 

888888888888888888888888888 

Cement per Cu. Yd. 
Concrete, Using 
Pit Run Gravel 

qqa 

OS' 1$ JSO ,0 

(ID 

i i 

C<!t~fc-LQ''H<Ne<3QO'^CSOO'*iilC>QD l NiN lt'Nt~CO<N<N<?3'ai<N 1 
0 )lOO»HOW«HIN»H(CliONM it'Oii-ieoC'JCOOClO-^ l 

i i 

•siqa 

S' 

rH 

i i 

ooooi»(»Minifliyci5in5MO®oocQ icoisioiooou^iocijin i 

Ir-llB-tflO-ailOINIIN© 1 

ci3<Ncococ<SMcoe<Jc*i<NcoiN>eococ<5<N lojcocorHeiiMcijcoiN i 

sjjaag 

'—' 

O Q Q C> O O O O O O O O O O O O lOOOOQOQOO « 

H ir) io 'VJ ^ H (M H 1^ H Uj HI <M O lO lt^<NOO(MO<N^O)CO • 

. .. 1 . 1 

O^CiiCO<MCCO?rf<HHC 0 rH(M(J 0 (>l(MCOrH K>]HOOCCO^CO(MH 1 

rH rH i— i rH rH rH rH rH rH rH rH rH rH rH rH 1 rH rH rH rH rH f-' rH rH 1 

i 1 

i «;0 jo oStuuaojaj 

/—V 

00 

w 

M-#MWNMHS)C4C>O'4iC'JQ>f350Me0MHMOO!9QO!M 

co^Osi'OOO^W't'w^w'SiM'O'CcOHt'Ttiwocoxoin 

in d r4 r-i H co rl rn o d <n" 6 d io ® d ^ o m’ h d (d si <o m h 

rH CH !-( r-l 

I 

Voids 

auojg 

8 

00 © 03 GO TH ! OO^^I^O^QO^Ol^cv^OOTOJt-rOQco^Jt:—COC^ 

Cj ^ CO '•H iC^CO'^'^^fiOC^COH^COCQCgCOCOCOOQ'^COCOtO 

pUBg 

g 

coe '2 4>00^<0'a<^®C>l>'4'QOOc<iecifOOO^«gcOCaOQtft«C>C^ 
SO - ^ | 40'4 ( Mfr34*5COCO<SiCO?OCOCOCO'^C003COC<3C»iC<3coiOCOCOCO 

auojg oj 
puBg jo oijBg 

/H 

to 

V-' 

S88S8e ;88888$38£jS8 8,88 1^8883 

r-i in' d d H d id^'^o^ddo'itiooo ic^oo iwo^o 
i—1 HrlWH i»4l IN JfO ^ IHri 

I I 1 

uaajog 
'nr 91-1 SaissBa 
puBg jo eSBjuaajaa 

/—\ 

fc8BB883588ffi8ffig«S$S8888S888teffi3 

rn rH 

(•ui 8-1 Smssea) 
pueg jo eSejuaajaji 

/'—S 

CO 

w 

$5^8d8o888888feSSoor5®8c3^'^8S®^iH 

rH rH rH 

(•ut 8-1 eAoqy) 
auojg jo oSBjcaaJOd 

/—N 

<N 

>w/ 


jaqmnK aidiues 

e i 



* 


Sand to add. 






























































































20 


Group 3, listed in Table IV, contains pit run gravels of such 
a character that both the % inch and 14 inch sands screened 
from them is so poorly graded that it is inadvisable to use the 
material as gravel on work of any importance without their 
being reproportioned or being mixed with other pit run gravels 
that will correct the deficiencies in their grading. Most of them 
are sands and could be used as such if coarse material were 
added. 

Cleanness. In all the discussion of pit run gravels it is as¬ 
sumed that the material does not contain an excess of clay or 
loam. The percentage of clay by dry measure should not ex¬ 
ceed 3% for reinforced concrete work and 5% for mass concrete, 
not reinforced. 

If concrete is to be used for work where weight is the prin¬ 
cipal requirement and where the load in compression does not 
exceed two or three hundred pounds per square inch, then any 
of the pit run gravels of the types of those in Tables II, III 
and IV may be safely used if the proper amount of cement is 
added. If, however, gravels are used in reinforced concrete 
where the loads in compression may reach six or seven hundred 
pounds per square inch, much more care should be exercised 
and the concrete should be proportioned as discussed in con¬ 
nection with Tables II, III and IV. 

Quantity of Gravel Needed for a Cubic Yard of Concrete. 

The exact amount of pit run gravel necessary for one cubic 
yard of rammed concrete is hard to specify since it will depend 
partly upon the dryness of the gravel when measured and partly 
upon whether it is measured loose or packed. It is assumed in 
the following discussion that a cubic yard of pit run gravel, 
loose measure, makes one cubic yard of concrete. It is also as¬ 
sumed that if sand and stone are measured separately and re¬ 
mixed for making concrete it will require 0.42 cubic yards of 
sand and 0.84 cubic yards of stone for one cubic yard of con¬ 
crete. This is not exactly true for all mixtures but is nearly 
so for ordinary mixtures where the quantity of stone is specified 
as twice the quantity of sand as in 1-2-4 or 1-3-6 concrete. 

REPROPORTIONING GRAVELS. 

As an illustration of the foregoing discussion let it be as¬ 
sumed that concrete is to be made from pit run gravel on work 
for which the specifications provide for a mixture of 1-2-4, but 
permit the use of pit run gravel if cement is added in such a 
quantity that the mortar meets the specifications. If the pit 
run gravel contains more sand than is required there are three 
alternatives: 


Cubic feet of Pit Pun Gravel'per Sack of Cement 


21 



* 






<0 




N 


03 


1. To add cement so that the mortar will be of the specified 

strength, that is 1 part cement to 2 parts sand. 

2. To screen the gravel and discard the surplus sand, in 

which case the smallest amount of cement would be 
used. 

3. To add broken stone to the pit run gravel so that the 

specified ratio of sand to cement would be main¬ 
tained as well as the ratio of sand to stone. In this 
case the same amount of cement would be used as 
in (2). 

Which of these three methods will be followed will depend 
upon their relative cost and that will vary with the relative cost 


* >,* 


Number Sacks of Cement per cubic yard of Concrete 

FIGURE 5 



























































































































































































































































































































































































































































































































22 


of the various materials and the percentage of sand in the 
gravel. The following analysis and discussion of a sample ot 
pit run gravel will illustrate the manner in which the most eco¬ 
nomical method of mixing can he determined. 

Cost With Fit Run Gravel. Let it be assumed that the pit 
run gravel has been analyzed and has been found to contain 
60% of sand and 56% of stone and is to he used without repro¬ 
portioning. The amount of cement to use for one cubic yard 
of concrete is y 2 of the amount of sand in one cubic yard of 

27x0.6 

the pit run gravel or -=8.1 cubic feet. Since 1 sack of 

2 

cement contains 0.95 cubic feet, the number of sacks of cement 
8.1 

to use is-=8.52 

0.95 

The amount of cement required for 1-2-4, l-2y 2 -5 or 1-3-6 
concrete can be determined from the curves in Figure 5, if the 
per cent of sand in the pit run gravel is known. Using the case 
mentioned above as an example and referring to Figure 5, find 
the percentage of sand at the left of the diagram and follow to 
the right to the curve marked 1-2 mortar, and read at the bot¬ 
tom of the diagram the number of sacks of cement, in this 
case 8.52. In like manner the amount of cement may be deter¬ 
mined for any other percentage of sand, and for any of the 
three mixtures given in the diagram. 

In comparing the economy of different methods of propor¬ 
tioning, the quantity of cement per cubic yard of concrete is 
the information desired. When the pit run gravel is used it 
is desirable to know the amount of gravel in cubic feet that 
must be used with 1 sack of cement, so that the proper quantity 
can be placed in the mixer. 

Since 27 cubic feet of the above pit run gravel is to be used 
with 8.52 sacks of cement, the amount of gravel to use with one 

27 

sack of cement is -=3.16 cubic feet. This quantity can 

8.52 

also be determined from the diagram in Figure 5 as follows: 
Find the percentage of sand at the left of the diagram and fol¬ 
low to the right to the curve marked “ Cubic feet of pit run 
gravel to use with one sack of cement, 1-2-4 mixture” and read 
at the top of the diagram the number of cubic feet of pit run 
gravel, in this case 3.16. In like manner, the quantity can be 
determined for any other percentage of sand and for either of 
the three mixtures given. 





23 


If cement costs $1.50 per barrel and the pit run gravel costs 
25c per cubic yard, the cost of cement and the above gravel per 


cubic yard of concrete is: 

8.52 

Cement -xl-50=.$3.19 

4 

Gravel . 0.25 


$3.44 

The cost for cement and aggregate may also be determined 
from the diagram in Figure 6. At the left of the diagram find 
the percentage of sand which in this case is 60, and follow to the 
right to the curve marked “pit run gravel at 25c per cubic yard” 
and read at the bottom of the diagram the cost for cement and 
aggregate for one cubic yard of concrete, which in this case is 
found to be $3.44. 

In the same way the cost for cement and aggregate can be 
determined for any other percentage of sand. If the mixture 
is l-2y 2 -5 the cost can be obtained from Figure 7 and if 1-3-6., 
from Figure 8. 

Cost With Screened Gravel. Having the cost of cement and 
aggregate for one cubic yard of concrete, using the pit run 
gravel, the next step is to find the cost of cement and aggregate 
for one cubic yard of concrete if the excess sand is screened out 
and discarded. Since the amount of sand required for one 
cubic yard of concrete is 0.42 cubic yards, and the amount of 
stone 0.84 cubic yards, the amount of the pit run gravel that 
must be screened to furnish enough stone for one cubic yard 
of concrete may be determined as follows: 

The amount of stone needed is 0.84 cubic yards and 1 cubic 
yard of the pit run gravel contains 0.56 cubic yards of stone, 

0.84 

therefore, the amount to screen is-=1.5 cubic yards. 

0.56 

The amount to screen may also be determined from the curve 
in Figure 9 as follows: Find at the left of the diagram the 
per cent of sand in the pit run gravel and follow to the right 
to the curve marked “Gravel to screen” and read at the bot¬ 
tom of the diagram the number of cubic yards to screen, which 
in this case is 1.5. 

In like manner the number of cubic yards to screen can be 
determined for any percentage of sand. The curve holds good 
when the amount of coarse aggregate is specified to be twice 
the amount of sand, regardless of the amount of cement specified. 

The cost of the aggregate for a cubic yard of concrete depends 
upon the cost of the pit run gravel, the cost of screening and 
whether the surplus sand must be paid for or may be left in 








24 



Cost of Cement and Aggregate fop a cubic card of /: C:4 Concrete 

FIGURE 6 

the pit and not paid for. Assume that pit run gravel costs 25c 
per cubic yard, that the surplus sand need not be paid for and 
that screening costs 30c per cubic yard, and that cement costs 
$1.50 per barrel, and the cost of cement and aggregate for one 
cubic yard of concrete will be as follows: The cost of cement 
will be as follows: Since 0.42 cubic yards of sand will be used, 
0.21 cubic yards of cement will be used, or 5.67 cubic feet, and 
since a barrel of cement is 3.8 cubic feet, the number of barrels 

5.67 

of cement required is-=1.49, or say, 1.5 barrels. 


3.8 

Cost of cement 1.5X1.50= $2.25 

Cost of 1 cu. yd. pit run gravel 0.25 
Cost of screening 1.5 cu. yd 0.45 


Cost of aggregate per cu. yd. $2.95 


If the surplus sand must be paid for it will add to the above 
the cost of 0.5 cubic yard sand discarded, or 12^c, making the 
cost of the aggregate for one cubic yard of concrete $3.07. 






































































































































































































































































































































































































































































































25 



FIGURE 7 

The cost of aggregates for a cubic yard of concrete when the 
percentage of sand is known and when the mixture is 1-2-4, 
1-2 y 2 -5 or 1-3-6 can be read from the diagram in Figures 6, 7 
and 8. 

These diagrams also give a curve of costs when all material 
screened must be paid for and are used in the same manner as 
the curves already described which are given in Figure 6. 

Cost When Stone Is Added. If crushed stone is available, 
it may be cheaper to add it to make up the deficiency in coarse 
material than to screen the gravel. To determine the quantity 
of stone to add for one cubic yard of concrete, the amount of 
the pit run gravel to use to furnish the proper quantity of sand 
must first be determined. Since it requires 0.42 cubic yard of 
sand for a cubic yard of concrete and each cubic yard of the 
pit run gravel contains 0.6 cubic yard of sand, the quantity of 
the pit run gravel needed to furnish sand for a cubic yard of 
0.42 

concrete is -=0.7 cubic yard. 


0.6 

























































































































































































































































































































































































































































































































26 


Since the pit run gravel contains 56% of stone, there will be 
in the 0.7 cubic yards of pit run gravel 0.7X0.56 or 0.392 cubic 
yard of stone, and since 0.84 cubic yard of stone is needed for 
a cubic yard of concrete it will be necessary to add to the 0.7 
cubic yard of pit run gravel 0.84—0.39=0.45 cubic yard of 
stone. The cost of the materials for one cubic yard of concrete 
will, in this case, be as follows, assuming the stone to cost $1.60 
per cubic yard: 

Cost of pit run gravel, 0.7X0.25= $0.17 

Cost of stone to add, 0.45X$l-00= 0.72 

Cost of cement, 1.5X$l-50= 2.25 


Cost material for 1 cu. yd. of concrete $3.14 

The amount of stone to add to pit run gravel containing any 
percentage of sand, to give material for one cubic yard of con¬ 
crete, can be obtained from Figure 9 by finding the percentage 
of sand at the left of the diagram and following to the right to 
the curve marked “Amount of stone to add to pit run gravel” 
and reading the quantity to add at the top of the diagram. It 
should be noted that if the sand content of the pit run gravel 
is less than 42%, then sand must be added as indicated in the 
diagram or some of the stone must be screened out of the pit run 
gravel and wasted. 

Now, having determined the cost of the aggregate for one cubic 
yard of concrete by each of the three methods of proportioning 
the pit run gravel under discussion, the most economical can be 
chosen. For convenience the three possibilities are summarized 
as follows: 

COST PER CUBIC YARD OF CONCRETE FOR AGGREGATE AND CEMENT. 

1. Use without reproportioning.$3.44 

2. (a) Screening out and discarding sur¬ 

plus sand and paying only for 

gravel used . 2.95 

(b) Screening out and discarding sur¬ 
plus sand, but paying for all 
gravel screened . 3.07 

3. Adding crushed stone. 3.14 

It will be seen that the cheapest method is to screen out and 
discard surplus sand, if only material used is paid for. If all 
gravel screened must be paid for it is still cheaper than to add 
stone, although the difference is slight. It is by far the most 
expensive to use the pit run gravel without reproportioning. 

Conclusions. The relative costs of the three methods out¬ 
lined will vary with the costs of materials and the cost of labor, 
and for any given set of conditions these costs must be worked 
out before a decision can be reached, as to the most economical 







Percent of Sand in Pit Pun Gravel 


27 



Cost of Materials for one cubic yard of /■' 3■ 6 Concrete 

FIGURE 8 

procedure. The quantities of materials can readily be deter¬ 
mined from curves shown in Figures 5 and 9 and the costs can 
then be determined when the price is known. 

A study of Figure 6 which applies to concrete mixed in the 
proportions 1-2-4 and with materials at the prices indicated on 
the diagram, shows that if the sand content of the gravel is more 
than 50% and less than 95% it pays to screen and reproportion. 
It also shows that it is much cheaper to add crushed stone than 
to use the pit run gravel. If the sand is above 80% it is cheaper 
to add stone than to screen if the surplus sand must be paid for. 
In the same way it can be seen from* Figure 7 that for 1-21/2-5 
concrete with materials at the prices indicated on the diagram, 
if the percentage of sand is less than 50% there is no great sav¬ 
ing to be obtained by reproportioning, hut if the percentage of 
sand is between 50 and 95 it will he a decided saving to screen. 
The diagram also shows that if all the material screened must be 
paid for, including the surplus sand, then if the sand content 
is greater than 75% it will he cheaper to add stone than to 
screen the gravel. 





































































































































































































































































































































































































































Cubic yapps Stone to adp to Pit Sun 6pavel to make a cubic yapp of Concrete 


28 



13AVBQ Nn^J-UJNtdNV$U0 ±N3033rf 


Similarly, Figure 8 shows that for a 1-3-6 concrete with ma¬ 
terials at the prices indicated on this diagram, it pays to screen, 
if the sand content exceeds 55% and is less than 93%. It also 


Numbef cubic yaepf Pit Pun Oeavfl to soften foe one cub/c yaep of Concrete 

FIGURE 9 












































































































































































































































































































































































































































































































































29 


shows that if all material screened must be paid for it is cheaper 
to add stone than to screen if the sand content exceeds 75%, 
and if only the material used is paid for it is cheaper to add 
stone than to screen, when the sand content exceeds 88%. 

These relations hold true whether % inch or *4 inch sand is 
used and the decision as to which size will be adopted for sand 
depends upon the size of the coarse aggregate as previously 
explained. 

If the 14 inch sand is used more cement will be required with 
pit run gravel than if y 8 inch sand is used, but in case of doubt, 
use the % inch sand. 

It should be noted that the typical cases worked out in the 
preceding pages give results which are comparable only when 
the prices paid for pit run gravel, crushed stone, screening and 
cement are as indicated. For other prices the quantities can be 
determined from Figures 5 and 9, the cost computed as outlined 
in the illustrative example. The computations are simple and 
the tests can readily be made in the field and adjustments in the 
methods of proportioning made in accordance with the tests. 

In this connection it should be noted that for concrete roads 
or pavements the pit run gravel should, in every case, be 
screened and the sand and stone thus obtained used for the 
concrete. Pit run gravel should never be used for concrete road 
or pavement construction. 


80 


*No. 1. 


*No. 2. 


*No. 

*No. 


3. 

4. 


*No. 5. 


*No. 

*No. 


6 . 

7. 

8 . 

9. 


*No. 
*No. 
*No. 10. 
*No. 11. 


BULLETINS OF THE ENGINEERING EXPERIMENT 

STATION. 

The Iowa State College Sewage Disposal Plant In¬ 
vestigations. 

Bacteriological Investigations of the Iowa State Col¬ 
lege Sewage. 

Data of Iowa Sewage and Sewage Disposal. 

Bacteriological Investigations of the Iowa State Col¬ 
lege Sewage Disposal Plant. 

The Chemical Composition of the Sewage of the Iowa 
State College Sewage Disposal Plant. 

Tests of Iowa Common Brick. 

Sewage Disposal in Iowa. 

Tests of Dry Press Brick Used in Iowa. 

Notes on Steam Generation with Iowa Coal. 
Dredging by the Hydraulic Method. 

An Investigation of Some Iowa Sewage Disposal 
Systems. 

II. No. 6. The Good Roads Problem in Iowa. 

Tests of Cement. 

State Railroad Taxation. 

Steam Generation with Iowa Coals. 
Incandescent Lamp Testing. 

Steam Pipe Covering Tests. 

The Assessment of Drainage Districts. 

Tests of Iowa Limes. 

Holding Power of Nails in Single Shear. 
Miracle Contest Papers for 1908. 

Miracle Prize Papers for 1909. 

Sanitary Examination of Water Supplies. 
Sewage Disposal Plants for Private Houses. 
Electric Power on the Farm. 

The Production of Excessive Hydrogen Sul- 
fid in Sewage Disposal Plants and Conse¬ 
quent Disintegration of the Concrete. 

A Study of Iowa Population as Related to 
Industrial Conditions. 

History of Road Legislation in Iowa. 

Costs of Producing Power in Iowa with Iowa 
Coals. 


•Vol. 

Vol. III. No. 1. 
Vol. III. No. 2. 
*Vol. ILL No. 3. 
Vol. III. No. 4. 
*Vol. III. No. 5. 
•Vol. III. No. 6. 
Vol. IV. No. 1. 
Vol. IV. No. 2. 
Vol. IV. No. 3. 
Vol. IV. No. 4. 
Vol. IV. No. 5. 
Vol. IV. No. 6. 
Bulletin No. 25. 
Bulletin No. 26. 


Bulletin No. 27. 

Bulletin No. 28. 
Bulletin No. 29. 


31 


Bulletin No. 30. 
Bulletin No. 31. 

Bulletin No. 32. 

Bulletin No. 33. 
Bulletin No. 34. 


The Determination of Internal Temperature 
Range in Concrete Arch Bridges. 

The Theory of Loads on Pipes in Ditches, 
and Tests of Cement and Clay Drain Idle 
and Sewer Pipe. 

A Topographical Survey of the Spirit and 
Okoboji Lakes Region. 

House Heating Fuel Tests. 

The Use of Iowa Gravel for Concrete. 


*Out of Print. 


s 























